Mechanical model of shear stress increasing process during initial deformation of gelled crude oil

Key words:  gelled crude oil  initial deformation  increasing shear stress  damage factor

Abstract:

Considering the creep and relaxation properties of gelled crude oil, a mechanical model was established by combining the Maxwell viscoelastic analog and a power-law dashpot in parallel. Constitutive equation of the mechanical model was figured out by introducing strain-dependent damage factor into the power-law dashpot and integrity factor into the Maxwell analog. Mechanical responses of Daqing and Nanyang crude oils were tested using rheometer under constant shear rates. The constitutive equation was used to fit the experimental data of shear stress increasing process. Stress relaxation processes under constant shear strain were calculated using the fitted model parameters. It has been found that the constitutive equation fits the data very well, and the parameters in the equation keep unchanged under different shear rates, which could be regarded to represent the actual properties of gelled crude oil. The proposed model can describe the relaxation properties of gelled crude oil theoretically. The relaxation modules decrease and the structure damage becomes greater with the increase of shear strain, which is consistent with the actual rheological properties of gelled crude oils.